The present invention is directed to the lubrication mold charge delivery systems and molds for forming glass objects from charges of molten glass.
In the manufacture of glass articles, such as glass containers, molten glass charges fed from a glass feeder are delivered to a parison or pre-form mold where the viscous charge is formed into the shape of a parison. The parison is then transferred to a final shaping mold where the parison is expanded into its final shape. It is known in the art of lass forming that the presence of a lubricant in the parison mold is desirable to overcome the adherent quality of the viscous glass and to allow the molten glass to slide relative to the mold surface. Further, lubricants have been used in the delivery systems for molten charges to reduce the frictional engagement of the molten charge with scoops and troughs which guide the charge from the feeder to the mold.
Traditionally the molds were lubricated with a carbonaceous liquid termed "mold dope". This "mold dope" was not always of uniform quality and many machine operators had their own concepts as to what should be included in the "mold dope". The "mold dope" was added to the mold by the insertion of a brush which had been dipped in the dope into the hot mold. This procedure also was characterized as "swabbing" the molds. The frequency of the swabbing was not a precise factor, but was usually left to the operator whose prime concern was to prevent the glass from sticking to the mold, either on entry as a gob or after shaping into a parison. Thus, swabbing was considered an "art" by the machine operators but typically the first ware produced after swabbing would have to be discarded because of defects.
Alternatively, semi-permanent mold coatings were used to provide the requisite lubrication in the molds; however, in time these coatings have to be reapplied.
A recently issued U.S. Pat. No. 4,526,600, issued to Myers, discloses a method for the lubrication of delivery equipment and molds for producing glass articles. This patent teaches the application of a lubricant to the viscous glass prior to its contact with the delivery equipment and/or prior to the introduction of the glass charge into the mold. The lubricant is applied to the glass at a location in the forming process which is prior to contact with the delivery equipment and/or molds. The lubrication means employed by the patentee were of the type where the mold charge or gob of molten glass either passed through the device, as shown in FIGS. 1, 5 and 6; or in the preferred embodiment of FIG. 2, the lubricant, in the form of a powder (e.g., powdered graphite), is applied to the glass gob by means of a flame spray lubrication means. The powdered graphite is introduced into the nozzle of a burner together with combustion gases for a flame. A plurality of burners aimed radially inward were symmetrically disposed around the coating zone. Three burners at 120.degree. intervals were suggested.
The suggested lubricants were powdered graphite, powdered inorganic salts such as sodium or potassium sulfate. The coating of the glass gob eliminates the need for specifically lubricating the interior of the mold or the delivery equipment since the lubricant will be transferred from the gob or charge to the surface of the delivery equipment and mold.
The term delivery equipment is intended to encompass gob chutes, funnels, guides, troughs or other charge directing or shaping members that are employed in guiding gobs by physical contact therewith during normal free fall of the gobs from the feeder to the molds.
"Molds" are intended to include any forming member in which the glass gob is received and in which the shape thereof is transformed while therein.
One problem encountered with employing the method of U.S. Pat. No. 4,526,600 was that the formation of mold charges would need to be discontinued in order for the equipment to be set up in surrounding relationship to the path of drop of the mold charges or the charges would have to be intercepted from the path and sent to a discharge chute. In either event, the operation of the forming process would be discontinued during the installation or implementation of the process of flame spraying graphite powder on the mold charges. When a process that involves hot glass is interrupted, the system requires a start-up time when resumed.